replacing kde-window-manager (and dependencies) from the version in jessie to the version in sid fixes the issue, however, it introduces other bugs so cannot be considered a fix.
Similar issues have been reported (and supposedly fixed) upstream - see KDE bugs 326352 and 329908, so it would seem that versions of kde-window-manager around 4.11.3 to 4.11.5 (or thereabouts) are problematic.
